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How To Choose Fish Tank Size: 10 Gallons Per Fish

Do you want to start keeping pet fish at home? This is one of the best hobbies that you can ever get into.

First, it makes you very responsible because you have something to nurture and take care of.

Secondly, it makes your home beautiful, having a glass or acrylic aquarium right where it will capture all the attention. Of course, the live fish are the main eye-catchers, with their graceful swimming.

But … before you can get to enjoy all of the above, you need to choose the right aquarium size. Keep reading!

Big or Small Fish Tank? Why Big Size Wins

A big fish tank is going to cost you a good amount of money. However, it is still much better than a small one.

A bigger aquarium can hold more water and more fish. Fish get their oxygen from the water, as it passes over their gills and body. Thus, the more water a fish tank can hold, the more oxygen your fish will get.

A big aquarium looks much better than a small one. You can also add many live aquarium plants, and they will look so stunning. They don’t make the fish tank look crowded at all.

When you get a small 5 gallon fish tank, you do not have much room for anything else apart from the fish and the water.

Here are other reasons why you need a big fish tank:

The water stays cool longer

When you have a large tank, the water does not warm up too fast. In another article on the best temperature for fish tank we said that warm water holds less oxygen. Thus, with a small tank, you have to change the water more often than you would a big aquarium.

The best size fish tank also depends on the type of fish that you intend to keep there. For example, marine/saltwater fish grow to bigger sizes than freshwater fish.

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Thus, if you are looking for the best tank size for saltwater fish, you will have to make it bigger. Some saltwater fish grow to large sizes. You can always go by the recommended minimum of 10 gallons of water per pet fish.

10 gallon vs 20 gallon fish tank dimensions

When you are starting out in keeping pet fish, you will be thinking about 10 gallon vs 20 gallon fish tank dimensions.

But first, some people ask: What size fish tank is easiest to maintain? Many sources say that a 5 gallon fish tank is easy to maintain. However, it is quite small. It will also require more water changes to keep the oxygen levels up in the water.

Thus, we recommend that you avoid the small tanks. It is best to go all out and buy at least a 50 gallon or bigger if you can. That is going to allow you to keep many fish and make a colorful aquarium.

So between the 10 gallon vs 20 gallon fish tank for beginners, choose the larger, 20 gallon one. If you get the 10 gallon tank size, you will probably feel the need to upgrade to a bigger one in future.

Some people also ask: how big is a 20 gallon fish tank? In liters, this is 76 liters.

If you want to introduce your young son or daughter to the fish keeping hobby, you can get them a small 5 or 10 gallon fish tank. You can then teach them how to do everything on their own. It will turn them into very responsible young people. This is definitely the best size fish tank for beginners.

Still on the size, for a freshwater fish, ensure that it has 10 gallons of water. A saltwater fish can grow really big, so it needs a 30 gallon water space.

Thus, the best dimensions for freshwater fish pet is 22 by 12 by 13.5 inches. For a saltwater fish, the tank dimension should be 36 by 18 by 12 inches.

The space available

How to choose fish tank size also depends on the space that you have available at home or at work.

If you have a big space where you want to keep your aquarium, a big one will be very appropriate. If you have a bigger space, you will need a bigger fish tank.

If you have a small space, you will need a small fish tank. It is all about balance. If you have too much water in the room, that is considered bad or negative feng shui.

Since you want the fish tank to be the main center of attraction, you need the best aquarium size. Thus, small room needs fish tank small size and big room needs a big tank size.

If you put a small fish tank for a big room, it will not stand out. There will be no point in having the fish aquarium.

The type of fish you want to keep

While we have mentioned that saltwater fish need a bigger tank and freshwater ones need a smaller one, you might have to buy the species of fish that is most appropriate for the tank size that you have.

Betta fish, Dwarf Puffer, Least Killifish, Bumblebee Goby and Sparkling Gourami are some of the small fish that you can keep in small fish tanks. They do not grow too big.

All the same, make sure that the fish have enough space to flourish. Remember, oxygen in the water is also depletable, so the more fish you have, the faster they will consume the oxygen.

Just to give you an idea, the best size aquarium for 1 betta fish should be a minimum of 5 gallons, nothing less! Consider that a Betta fish grows to about 3 inches, so it is pretty small. Thus, for bigger fish, you will need a bigger tank size.

How big is a 100 liter fish tank?

If you are beginning your fish-keeping hobby, you might be considering a 100-liter fish tank. But just how big is a 100 liter fish tank?

In gallons, this is about 26 gallons, which is quite a small as much as tanks go. Depending on the type of fish that you intend to keep, you can go bigger on the tank.

Medium sized pet fish such as Snakeskin Gourami can grow to as long as 20 inches. Thus, you might be able to keep up to five of these fish in the 26-gallon fish tank.

How big is a 100 liter tank? For Betta Fish, Snakeskin Gourami and Goldfish, this is big enough. You can also get smaller saltwater fish such as Mollies that grow to a maximum of 5 inches, or even Garibaldi fish that grow to up to 15 inches.

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Basically, before you can decide whether a certain fish tank size is good enough for you, find out all the information about the fish species that you want to keep.

Afterward, you can buy an appropriately sized tank.

Do fish grow according to tank size

As you seek to know how to choose fish tank size, you might also wonder: do fish grow according to tank size?

Nothing could be further from the truth. A fish will only grow to its maximum size. If it does not grow to its adult size, it must be stunted from lack of nutrients, enough oxygen or it might have some other problem.

Thus, when buying a fish tank, just consider the maximum adult size of the fish that you intend to keep.


The market teems with many fish tanks that come in different sizes, shapes and styles. Whether you want a 20 gallon tank size, 50 gallon, 70 gallon or even bigger, they are all available.

Remember, bigger is better, and costlier. You will also need to have a bigger and more steady platform to hold all that weight for many days. Remember, 1 gallon is equivalent to 3.8KG and that’s heavy!

That is it for how to choose fish tank size. Enjoy your fish keeping.

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